The present invention relates to liquid dispensers. More particularly the present invention relates to a multi-channel liquid dispenser capable of dispensing very small volumes of fluid.
Pharmaceutical, combinatorial chemistry, high-throughput screening, and medical diagnostics applications, among others, require dispensing very small volumes of liquid (i.e., nano-liters to micro-liters) into a receiver such as a micro-titer plate. It is usually necessary to perform the dispensing operation without cross-contamination, which might occur, for example, if a reagent is being added to a receiver that already contains another reagent.
To substantially eliminate the incidence of cross-contamination, a xe2x80x9cnon-touch offxe2x80x9d method of liquid dispensing is typically used. In this method, a droplet being dispensed does not contact the receiver (or liquid or other material in the receiver) until the droplet completely disengages from the tip of the dispenser. Non-touch-off dispensing requires supplying enough kinetic energy to a liquid droplet for it to overcome the surface tension of the dispensing tip and enough kinetic energy so that it can be accurately and reliably directed to a desired destination.
Non-touch off dispensing of liquid volumes between about 0.1 to about 5 micro-liters is performed using either shake-off methods or implemented with various valve mechanisms that apportion the dispensed volume. While the use of valves for this service is straightforward in principle, it is rather difficult to implement in practice.
One valve-based prior art technique dispensing technique is the xe2x80x9cpositive displacementxe2x80x9d method. In this method, liquid is pressurized into a valve, typically using a syringe or pump, while a synchronized valve controller opens and closes the valve to expel the liquid. This technique has several drawbacks.
First, the accuracy of the dispensing operation is highly dependent upon the precise coordination of all controls, and is a strong function of the elasticity of the liquid channel and temperature. Moreover, accuracy is affected by the presence of trapped or internally released gas bubbles.
Second, this technique suffers from an unavoidable drop in liquid pressure during each dispensing cycle. As a consequence of the pressure drop, only a portion of the liquid that is advanced to the valve for dispensing each cycle is actually dispensed. This drop in pressure is caused by the delay between pump/syringe action and high-speed valve operation. While certain feedback and sensory elements can improve or at least monitor the operation, the design and implementation of the system becomes quite complicated.
There are some additional drawbacks that affect most prior art liquid dispensers regardless of operating principles.
For instance, in most prior art liquid dispensers, liquid travels a relatively large distance through tubing, etc., to reach the dispensing valve. This long travel distance might result in changes in liquid volume due to temperature/viscosity fluctuations, internal gas bubbles, elasticity variations of the tubing, and the like. Moreover, long tubing runs generally result in reagent losses during priming, cleaning and servicing operations.
Furthermore, most prior art liquid dispensers (especially multi-head liquid dispensers) are expensive. The expense is related to, among other elements, relatively complex positioning devices that position the dispensing heads.
There is a need, therefore, for a liquid dispenser that is capable of high-speed liquid delivery and is simpler, more reliable and less expensive than existing dispensers.
In accordance with some embodiments of the present invention, a multi-channel fluid dispenser that avoids some of the problems of the prior art is disclosed.
In the illustrative embodiment, a multi-channel fluid dispenser includes a reservoir, a multi-channel liquid dispensing head, a plurality of fluid-delivery conduits, and support and positioning elements.
The reservoir advantageously has multiple internal chambers for segregating liquid within the reservoir, as well as a non-compartmentalized region that overlies the chambers. The non-compartmentalized region facilitates an even distribution of pressure within the reservoir, thereby promoting the balanced dispensing of liquids from the various chambers.
The fluid-delivery conduits receive liquid from the chambers in the reservoir and deliver it to the dispensing head. The support and positioning elements are operable to support and position the dispensing head so that it can deliver the liquid from the reservoir to an underlying receiver.
In some embodiments of the invention, the multi-channel liquid dispensing head includes a valve-support member, a plurality of valves and a plurality of nozzles. The multi-channel liquid dispensing head is supported by a positioning member that engages the valve support plate.
The multi-channel liquid dispensing head is advantageously movable along three-axis to facilitate alignment with an underlying receiver. In one embodiment of the invention, elongate holes in the positioning member and elongate holes in the valve-support member cooperate to provide two-axis positioning. A separate positioning mechanism provides movement along the third axis.
In one embodiment of the present invention, the valves are attached the valve-support member by a fastener, such as a nut. The valves are received by an eccentrically-disposed hole in the fastener. Due to the eccentrically-disposed hole, as the fastener is rotated, the valves tilt relative to the vertical and the liquid dispensed from such tilted valves is directed at a non-normal angle into a receiver.